Layer & Bookmark view not initialized correctly on restart

The layers view is not populated correctly if not visible when restarted. To reproduce:
1. Create a map with at least one layer
2. Click on the "Bookmarks" view to 'hide' the layers view behind the bookmarks view
3. Restart uDig
4. Click on the Layers view; no layers will be shown

This bug affects both the layers and bookmarks views.

This is a result of the new MapEditorWithPalette. The layers view (and bookmark view) checks for a instanceof MapEditor when initializing the current map. I have a fix for this that makes use of IAdaptable which I will provide via git.